Each year I grow hundreds of plants from seeds including flowering annuals and perennials, dozens of heirloom and hybrid vegetables, and a wide variety of tomatoes. Most of these plants are started from seed indoors under my grow lights.
What began as a means to save money turned into one of my most enjoyable hobbies as well. See Seeds 101 to understand the various types of seeds.
How to Start Seeds Indoors for Indoor and Outdoor Plants
I’ve gathered all my best tips and tricks to give you everything you need to know to start seeds indoors.
Here’s the plan:
Read this post, decide what you want to grow, grab a couple of packs of seeds—you can find organic seed companies listed here— and get started!
If you want to see the supplies I used, they are listed here: Best Seed Starting Supplies.
Seed Starting 101
1. Plan Ahead
- If you’re interested in starting plants from seed, you may already have some ideas of which plants you’d like grow.
- I select non-invasive (suitable for my area) plants I love, and focus on ones that are either impossible to find at garden nurseries or cost a fortune to buy.
- Most seedlings prefer temperatures between 60-80F, so there’s probably several areas in your home that would be suitable for a grow light shelf unit (more on this below).
- You’ll also need to think about quantity since most of us have fairly limited spaces indoors for grow lights and shelves.
- At first the seedlings don’t take up much space, but as they grow, they’ll need larger pots.
- Figure out how many 3″ pots you can fit under your lights. I find that one 48″ light unit (2 bulbs) can service approximately 36 pots. The shorter 36″ lights will obviously cover fewer pots. Multiply by how many units you have. Add 10% (allowing for some seedlings to die off) and that tells you how many seeds you can start.
For example, if you have 4 (48″) lights = 36 pots each x 4 = 144 pots + 10%= start 158 seeds and end up with 144 plants.From there, determine how many of each type of plant you want to grow and start researching your seed source options.
2. Seeds Sources
- There are a lot of wonderful seed companies to choose from. Find sources in your own area whenever possible: this way you know the plants can thrive in your gardening zone. I have a list of some favourite seed suppliers here.
- Read the seed packets and/or seed catalogues.
Most seed companies provide a tremendous amount of useful information there including:
- Any preparation the seeds need, such as presoaking or chilling in the fridge before planting, or scarifying (scratching the seed surface). Don’t worry though – most just get planted without any prep.
- How deep to plant the seed in the growing medium.
- Whether the seeds like warmth or cooler temperatures, and lightness or dark to germinate.
- When to plant the seeds in relation to your estimated last frost date.
- How long it should take from seed (or planting outside) to harvest.
- Germination rates (how many seedlings should survive).
3. Supplies For Starting Seeds Indoors
Besides the actual seeds, there are some other supplies you’ll need.
- Pots, containers, and seed starting trays Use whatever you have and be sure to clean and disinfect them with diluted bleach between uses.
- Growing medium for seed starting, and/or compost and soil (see more on this below).
- Grow lights and shelving (see my setup and all the details here).
- Waterproof tarp – place it under and around the grow light shelves to protect your flooring from water and dirt spills.
- Plant tags [Or use my tag-free system.] Once you’ve planted seeds a few times, you’ll start recognizing the seedlings by sight- each type looks different.
- Pen and paper for notes.
- Watering can.
- Soil blocking tool, – a good investment if you plan on starting a lot of seeds each year.
- Garden heating pad -to add some warmth underneath the plant trays.
There are two options for starting seeds:
- Organic potting soil intended for containers or
- Seed starting growing medium.
They call it ‘growing medium’ because it doesn’t actually contain garden soil. I use both growing medium and organic potting soil—whatever is cheapest at the time.
- If you start the seeds in growing medium, they’ll need to be transplanted into larger containers with organic potting soil after a few weeks when they have their true leaves. Until then, seeds contain all the nutrients they need. Pretty cool!
Make Your Own Growing Medium
- A common recipe is 1 part each of peat or coconut coir, vermiculite, and perlite. If you are buying a prepared growing medium, be sure it is organic and food safe.
- Just like the commercial growing mediums, all of these items come with environmental concerns (because they’re either not sustainable and/or how they are extracted from the earth) and plastic packaging. Gardening is not very green at times.
Find out your first and last frost days and plan your seed starting accordingly.
Here’s what I do:
- I live in gardening zone 6 in southwestern Ontario Canada.
- I start my seeds indoors during February and March and plant them outdoors around mid-May after last frost of the season.
- I start my fall and winter seeds indoors in August and plant them outdoors in October before the fall frosts begin. The seedlings need time to establish strong roots before settling in for the winter.
Again, the seed packets often have good information for planning your schedule.
There are also several free online calculators for knowing what to plant when in your growing zone.
5. “Starting” /Planting The Seeds
Have your seeds, containers, growing medium or potting soil, watering can, and notes ready.
I plant one seed per cell, this way the seedlings will not have to be thinned later. Some gardeners plant a few as insurance (since some may not germinate).
- You’ll want your grow lights ready to go with the light height positioned approximately one inch above the top of your seedling containers.
- As the seedlings grow, you will gradually raise the lights up on their chains so they’re always about an inch away from the plant tops.
TIP: Don’t combine different seed types in the same container or tray or you’ll have a problem with varying heights under the grow lights—some seedlings grow quite tall and others are short and stubby.
- Keep track of what you’ve planted and in which containers. You can either prepare plant tags marking each one or use my easy no-tag seedling tracking system which involves marking the containers.
- Dampen the growing medium with water before planting the seeds. See my soil blocker post and short video for instructions.
- Check each seed package for specific planting instructions including how deep to plant the seeds in the growing medium or soil.
TIP: A seed’s size is often the best hint about how deep to plant it. Tiny seeds simply sit on the surface of the soil (needing light to germinate), larger ones get planted about 2-3 times as deep as they are wide (no light required).
- Plant all your seeds, noting what you’ve planted and in which container.
- Use a timer to keep the grow lights turned on for 8-12 hours per day.
- Check your seeds daily. You’ll be amazed how fast some of them will pop up – can be as quick as a day or as long as a few weeks, depending on the type of seed (the seed packages should tell you what to expect).
- Water the growing medium or potting soil just enough to maintain an even moisture level (not dripping wet or so dry the medium is crumbling). Always apply the water to the growing medium or soil, preferably around the base of the soil blocks, not directly on the seedlings.
- Keep the grow lights 1” above the tops of the seedlings.
- Allow air circulation in the room. If it’s muggy, use a fan. Seedlings grow stronger from gently blowing air. You can also run your fingertips across them to help strengthen them. A breeze also deters white flies.
- Keep notes on the growth progress – this becomes invaluable for next time. I like to take photos too.
Seed Failure and Staggered Sowing Schedule
- Sometimes seeds just do not germinate, or, they start and suddenly stop growing and die. It could be bad seeds or the batch simply didn’t like the growing conditions. Don’t freak out or declare a brown thumb. Every grower has hits and misses. That’s life, baby.
TIP: For favourite plants like heirloom tomatoes, I start a few backup crops every week or two so I’ll have spares in the event that one batch fails.
- I do not add fertilizer to my seeds or seedlings. I find that organic potting soil is sufficient.
Write It Down
- Make notes of everything you do so you can figure out what works best for the future.
I keep a spreadsheet (yes, I’m that nerdy) noting:
- The name and source of the seeds
- How I prepared the seeds
- Date planted
- When they started to germinate (how many days it took)
- When I transplanted the seedlings to pots
- How the plants do under the grow lights
- When I start hardening them off (introducing them to the outdoors, a few hours a time)
- When they were planted in the garden and I add an outdoor plant tag telling the dates I should expect the harvest (food crops)
- When the food plants were ready to eat and how delicious (or not) they were
- Any pests, diseases, or problems encountered
- Best ideas and tips for next time
Potting Up and Thinning Out
- Prepare your notes and have your plant tags ready before you start potting up. You’ll want a way to keep track of each seedling in its new pot.
- When seedlings have their first 1-2 sets of true leaves, after the initial cotyledon leaves, they are ready for a richer soil and a larger container. If you’re using soil blocks, you can move the entire block with the seedling into larger soil blocks or plant them in containers. Easy!
- If you’re using containers, moisten the potting soil with water so it’s damp but not dripping, fill up your pots, and gently transplant the seedlings to their new homes.
TIP: Seedlings should be handled by the true leaves, never the stems. I find the replanting of seedlings to be the most fussy part—that’s why I like soil blocks better: you never have to handle the seedlings directly.
- Some use a pencil or chop stick to gently make room for (poke a hole in the soil) and then guide the seedling into the new pot. If you’re good at this, you should be a surgeon.
7. Hardening Off and Planting Outdoors
- Hardening off simply means getting your seedlings acclimatized to life outdoors.
- I start 2 to 3 weeks before the estimated last frost date.
- During the days, I place all the containers in deep plastic tubs and set them out on the covered patio. Theoretically you want to increase their exposure to the elements a little more each day, but in reality, I tend to leave them out for about 6-8 hours and then bring them in overnight.
- As the weather warms, I leave them out longer until eventually they stay out 24/7.
- When conditions are favourable, I plant everything in prepared garden beds and containers.
- All of the seedling containers are then washed, rinsed with diluted bleach and water, dried, and ready for next time.
Saving and Storing Seeds
- I keep my seeds in the cool, dry, dark basement. I have envelopes arranged in alphabetical order by plant type (you can see my simple system here).
TIP: You can also save seeds from many of your own plants. You’ll need to know which plants produce true seeds (not hybrids). Mark your best plants and blossoms with ribbons: it is these particular flower heads that will produce the best seeds for saving.
Happy growing. If you have any questions, leave them in the comments. And please share this on Pinterest, Facebook, or Twitter if you enjoyed it.